Mythos is the mysterious leader of the hacker group Logos, providing Willwears to unstable or desperate people in order to provoke chaos, and the self proclaimed enemy of Unit 8. He's shown to be quite the formidable hacker and both Rin and Madoka was surprised at his skill. He is the main antagonist of this series.

Mythos appears to be very calm and collected in most situations and is usually seen smiling.

(Source: Active Raid Wikia, edited)